How to modify HTML of specific node in Drupal 7?

Question

I use Drupal 7 with Bootstrap Theme. I have many blocks placed on different nodes and HTML generated is as follows:

<div class="region region-content">
  <section id="block-system-main" class="block block-system clearfix col-md-12">
    <div id="node-21" class="node node-pagina clearfix">  
      <div class="content">
        [...]
      </div>
    </div>
  </section> <!-- /.block -->

  <section id="block-block-13" class="block block-block contextual-links-region clearfix col-md-4">
    [...]
  </section> <!-- /.block -->

  <section id="block-block-12" class="block block-views contextual-links-region clearfix col-md-6">
    [...]
  </section> <!-- /.block -->

  <section id="block-block-15" class="block block-block contextual-links-region clearfix col-md-12">
    [...]
  </section> <!-- /.block -->

  <section id="block-block-14" class="block block-block contextual-links-region clearfix col-md-12">
    [...]
  </section> <!-- /.block -->
</div>

I want to change that HTML for put some <div class="container"> to enclosing some <sections>

Example:

<div class="container">
    <section id="block-block-13" class="block block-block contextual-links-region clearfix col-md-4">
      [...]
    </section> <!-- /.block -->

    <section id="block-block-12" class="block block-views contextual-links-region clearfix col-md-6">
      [...]
    </section> <!-- /.block -->
  </div>

Answer 1

Short answer: Place a customized template named node--[nid].tpl.php or page--node--[nid].tpl.php in your themes template folder. ([nid] = id of specific node).

Long answer: If you didn't done yet, you should first create a Bootstrap subtheme for your modifications. Then copy either node.tpl.php or page.tpl.php from the Bootstarp theme inside your subtheme folder. Rename the file to either node--[nid].tpl.php or page--node--[nid].tpl.php (Replace [nid] with the node id of the specific node) and customize the file to your liking. Lastly clear the cache at /admin/config/development/performance

For more/other template examples have a look at Drupal 7 Template (Theme Hook) Suggestions

EDIT: To control specific blocks for a specific page, I'd create a dedicated region inside your subtheme's .info-file and in your page.tpl.php / page--node--[nid].tpl.php. And place the blocks inside those regions.